The present invention relates to a roll depletion monitoring device, for use in particular with wrapping machines.
In particular, the present invention relates to a monitoring device such as can be utilized to sense the stage at which a decoiling roll of strip material is near to final depletion, and thereupon pilot the operation of a control unit, for example a unit that will respond by replacing the depleted roll with a new roll.
The art field of automatic wrapping machines embraces the use of devices able to detect the approaching end of a roll of strip material when nearing full depletion and indicate the condition to a control unit, by which the spent roll is then replaced with a new roll automatically.
By way of example, European Patent no 155 020 discloses a monitoring device equipped with electromagnetic transducers able to sense electric or magnetic fields generated in the vicinity of the roll decoiler bearings.
Other types of electromagnetic transducers are sensitive to variations in an electric or a magnetic field generated by way of metallic bands associated with the wrapping material, either applied to short lengths of the surface afforded by the terminal portion of the strip, or spliced on and forming the endmost coils of the roll. Roll changer units have become more effective, functional and precise in operation since transducers of this type came into use, albeit problems have also been created for manufacturers and users of the rolls of strip material in question. Whatever may be the nature of the fillet or band of metallic material adopted as a means of exciting the transducers, in effect, it must be calendered together with and form an integral part of the strip material. This gives rise to a further problem, namely, that when the wrapping material is cut and then trimmed, the resulting waste is a composite material, that is to say comprising both wrapping material and metallic material, that cannot be recovered and recycled.
The object of the present invention is to provide a device such as will detect and indicate the final depletion of a roll of strip material without any need to apply metallic indicators, be they fillets, bands, leaders or whatever, so that the roll consists entirely of a homogeneous and easily recycled material.